Recently, various bonding materials have been used for applications such as fixing of electronic parts. The applications of this kind require not only strong adhesion but also high heat resistance such that the bonding material can withstand solder reflow in mounting an electronic part on a substrate. With miniaturization of electronic equipment, the adhering area has a tendency to become minute. In this case, the control of flowability (protrusion of adhesive) becomes significantly important from the problems of appearance and functional reductions of electronic parts. Further, in the applications of this kind, the adhesion treatment is generally carried out by heat pressing for securing the wettability in adhering, and the adhesion has been desired to be conducted under low pressure for a short period of time for improving the productivity and reducing damage of parts in heat adhering.
To such a request, JP-B-3-44592 (the term "JP-B" as used herein means an "examined Japanese patent publication") and JP-B-7-15090 propose that photopolymerizable compositions prepared by adding epoxy resins and curing agents therefor to photopolymerizable monomers comprising esters of (meth)acrylic acid and alkylene oxide addition products of alcohols or phenols or esters of (meth)acrylic acid and non-tertiary alcohols are irradiated with ultraviolet rays to photopolymerize the above-mentioned photopolymerizable monomers, thereby obtaining thermosetting viscous adhesive compositions.
However, the thermosetting adhesives proposed above are tacky at ordinary temperatures, and bubbles are incorporated therein because of their stickiness in face adhesion by a press. Accordingly, they have the problem that separation and foaming occur at a temperature of 100.degree. C. or more by expansion of the bubbles incorporated. Furthermore, since the adhesives contain imidazole, dicyandiamide or polyamines as the curing agent for the epoxy resin, there is a problem in the storage stability that the curing reaction of the epoxy resin with the curing agent gradually proceeds during storage before or after photo-polymerization to deteriorate the adhesive characteristics.
The curing reaction of the epoxy resin with the curing agent is finally conductedat the time of use for adhesion. Even after this reaction, crosslinkage is not formed between the epoxy resin and the photopolymerized product obtained by photo-polymerization of the photopolymerizable monomers, thereby resulting in insufficient heat resistance. In the thermosetting adhesives proposed above, particularly, the thermosetting adhesive proposed in JP-B-3-44592, the epoxy resin is used in a large amount as the curing component. The unreacted low-molecular weight epoxy resin flows out at the time of heat adhesion by a press to cause adhesive protrusion, which results in disadvantages such as poor appearance.